Currently, the development requirements of mobile communication are being able to support higher data rate, better coverage and higher resource efficiency. In order to achieve higher data rate, next generation mobile communication system will employ transmissions with wider frequency bandwidth, while wider frequency bandwidth will bring greater path loss, which affects the network coverage. The relay technology is capable of enhancing coverage as well as balancing and increasing cell throughput; and a relay station has relatively small deployment costs in contrast to a base station, and therefore the relay is viewed as a key technology in the evolved system of Long Term Evolution (LTE), i.e., LTE-Advanced (LTE-A) system.
In a time division dual (TDD) LTE system, frequency resources are divided in unit of frame over time. FIG. 1a is a schematic diagram of frame structure in a TDD system according to the related art. As shown in FIG. 1a, the length of each radio frame is 10 milliseconds and contains 10 subframes, with the length of each of the subframes being 1 millisecond, wherein the subframes comprise uplink subframe(s), downlink subframe(s) and special subframe(s) which is also referred to as frame structure type 2 in LTE specifications. Depending on the different ratios of the uplink/downlink subframe(s), there are 7 configurations in the TDD LTE system, and the system can flexibly perform subframe configuration according to information such as uplink/downlink traffic in a cell. The 7 configurations are shown in Table 1 specifically, wherein D represents downlink subframe(s), U represents uplink subframe(s), and S represents special subframe(s). FIG. 1b is a schematic diagram of the structure of a special subframe in the TDD system according to the related art. As shown in FIG. 1b, an S subframe includes a part of downlink pilot time slot (DwPTS), uplink pilot time slot (UpPTS) and a guard period (GP) for switching between the uplink and the downlink. As an evolved system of TDD LTE, the TDD LTE-A system should ensure backward compatibility and hence will maintain the same frame structure as that of TDD LIE.
TABLE 1A table of subframe uplink/downlink configurationforms in the TDD LTE systemsubframeuplink/downlinksubframe numberconfiguration01234567890DSUUUDSUUU1DSUUDDSUUD2DSUDDDSUDD3DSUUUDDDDD4DSUUDDDDDD5DSUDDDDDDD6DSUUUDSUUD
In a TDD LTE Release 8 system, service data transmission and corresponding feedback information transmission meets a certain timing relationship. Take the uplink feedback of downlink service transmission as an example. At downlink subframe having subframe number n-k, a base station (or known as evolved Node B, i.e. eNB in LTE/LTE-A) transmits data, and at uplink subframe having subframe number na user equipment transmits the corresponding acknowledge/negative acknowledge (ACK/NACK) feedback information to the base station according to the data reception. In this case, k is defined according to the subframe uplink/downlink configuration and subframe locations of the TDD system, which is shown in Table 2 specifically.
TABLE 2A table of uplink feedback timing k value in the TDD LTE systemsubframeuplink/downlinksubframe number nconfiguration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4, 6———8, 7, 4, 6——3——7, 6, 116, 55, 4—————4——12, 8, 7, 116, 5, 4, 7——————5——13, 12, 9, 8,———————7, 5, 4, 11, 66——775——77—
When the relay station is introduced into the TDD LTE-A system, there is one more hop added to data transmission, i.e., the original communication mode of base station-terminal changes. Take a two-hop system as an example, the communication mode of a terminal which receives the services of a relay station changes to be a mode of base station-relay station-terminal. In this case, it needs to allocate part of the uplink and downlink resources for base station-relay station communication, i.e., a part of subframes are allocated for use by the communication between the base station and the relay station. These subframes are referred to as relay subframes and corresponding links are referred to as relay links or backhaul links (or Un interface and corresponding relay subframes can also be referred to as Un subframes or backhaul subframes). However, considering the interference problem, the relay station cannot perform transmitting and receiving simultaneously in same frequency resource, and in this case, if the ACK/NACK timing defined in the TDD LTE Release 8 specification is reused, some ACK/NACK feedback information of relay link may be lost.
Take subframe uplink/downlink configuration 3 of the TDD system as an example. If subframe 7, 8, and 9 are configured as downlink relay subframes and subframe 3 is configured as an uplink relay subframe, ACK/NACK feedbacks corresponding to data transmission in these 3 subframes are transmitted in uplink subframe 3, 3, and 4 respectively according to TDD LTE Release 8 specification. In this case, if the ACK/NACK timing defined in TDD LTE Release 8 specification is reused for relay link, ACK/NACK feedback information corresponding to data transmission in subframe 9 will be lost.